1. Field of the Invention
The present invention relates to an organic electroluminescence device and a method for manufacturing the same, and more particularly to an electrode structure of a thin film transistor of an organic electroluminescence device serving as a driving switch and a method for fabricating the organic electroluminescence device.
2. Discussion of the Related Art
In a multimedia age, it is required for a display device to be finer and larger and to express colors close to natural colors. There are limits to a conventional cathode ray tube (CRT) in offering a large screen of 40 inches or more. An organic electroluminescence device, a liquid crystal display device (LCD), a plasma display panel (PDP) and a projection TV (Television) and the like are developing at a high speed to be widely used in a field of high-definition images.
Among the above-mentioned display devices, the organic electroluminescence device is a device emitting light in the following manner; if electric charges are injected in an organic film formed between a cathode and an anode, electrons and holes in pairs become extinct to emit light. Accordingly, the organic electroluminescence device can be formed on a flexible transparent substrate such as plastic. Further, the organic electroluminescence device can be operated at a low voltage (below about 10 V) compared to a plasma display panel or an inorganic electroluminescence device. Further, since the organic electroluminescence device has advantages of relatively low power consumption and excellent color sensation, the organic electroluminescence device has been given attention as a next-generation display device. Further, in order to operate the organic electroluminescence device at a low voltage, it is important to maintain a very thin and uniform thickness (about 100-200 nm) of the organic film and stability of the device.
The organic electroluminescence devices are classified into a passive matrix type organic electroluminescence device operated under switch control of electrical signals and an active matrix type organic electroluminescence device operated using thin film transistors (TFT) according to a driving method of sub-pixels.
A conventional active matrix type organic electroluminescence device is described below.
In the conventional active matrix type organic electroluminescence device, a thin film transistor is formed on the transparent substrate. In this case, the thin film transistor includes a active layer having a source region, a drain region and a channel region, a gate insulating film, a gate electrode, an interlayer insulating film and source/drain electrodes. The source and drain regions contact with the source electrode and the drain electrode through contact holes formed in the interlayer insulating film and the gate insulating film, respectively.
Further, a planarization film is formed of an organic material on the substrate having the thin film transistor. Further, an anode is formed on the planarization film to be electrically connected to the drain electrode. Further, an organic light-emitting layer is formed on the anode electrode, and a cathode electrode is formed on the organic light-emitting layer. In this case, the organic light-emitting layer includes a hole transporting layer, red, green and blue light-emitting layers and an electron transporting layer.
In this case, the hole transporting layer includes a hole injecting layer and a hole transfer layer. The electron transporting layer includes an electron transfer layer and an electron injecting layer.
However, the above-mentioned conventional organic electroluminescence device has the following problems.
In the conventional active matrix type organic electroluminescence device, the thin film transistor can be exposed to X-ray or the like in a deposition process of an anode, a light-emitting layer and a cathode, thereby causing damage to the thin film transistor. Further, there is a problem of reducing an electrical contact between the source/drain electrode layers.